Radio is a peculiar form of communicating, in that it is one of the very few mass communication media that is perceived strictly as a one-to-one medium. It is important to keep this in mind, both with how you write the copy that is going on air, and the type of language you use: Unlike any other media, you can actually speak directly to a radio listener without it feeling un-natural.
Of course, only a minor proportion of the world's population ever gets on the radio. Podcasting, however, is a different matter altogether: Podcasting.net, one of the largest podcasting directories in the world, is the harbour of roughly 35,000 podcasts, showing that this genre of radio is taking off on a serious way. Seeing as how podcasting is merely a smaller-scale, on-demand version of radio, all the tips in this write-up are applicable.
Writing clear scripts
The 1st step of presenting information via the radio is the copy. It has to be clear, use relatively short sentences, and be as informal and conversational as possible. Some broadcasters find it easiest to not write radio scripts at all, but concentrate on getting the facts and structure down on a piece of paper. Generally, it is recommended to have a clear script to work from.
The first thing to think about is timing: How many minutes of airtime do you wish to occupy? The rule of the thumb is that you use 3 words per second (wps) in radio. This means that a 300 word piece will take 1 minute and 40 seconds to read, or that you can assume around 180 words per minute (wpm). Bear in mind that it is very easy to read a lot faster than this: A normal conversation is generally around 200 wpm, and quick drum and bass MCs such as Daddy Freddy can hit speeds of 550 syllables a minute for a full minute - that's around 320 words per minute.
Writing a clear script can be a long process, as most written pieces are not meant to be read out loud. I recently spent a bit of time trying to read out a short story called "Standing on a mountaintop in northern Siberia under the rapidly descending bulk of asteroid McAlmont, with a calculating expression and a baseball bat", written by Sam512. The first paragraph goes something like this:
Twenty-five years ago they spotted it, fifteen years ago they plotted it, and five years ago they tried to stop it, but the nukes weren't enough. And there was no time or technology to try anything else. Two years ago the spot in the Urals where the asteroid 17045-2003AF is going to hit was narrowed to a hundred-metre square, and the evacuation began. Now humanity, huddling far below the horizons around me as the red glow overhead slowly grows, is a few minutes away from almost total incineration. The hammer of God is coming.
Re-writing this to readable copy would be a complicated task, mostly because the author placed every word in its right place for a reason, and re-shuffling and re-writing it into a radio script would be most disrespectful. It can be done, however, and will serve as a learning-by-example exercise:
Twenty five years ago they SPOTTED it. Fifteen years ago they PLOTTED it. And FIVE years ago they tried to stop it, but the NUKES were not enough. There was no time OR technology to try anything else. Two years ago, the spot in the you-rals where the asteroid seventeen oh fourty five DASH two double oh three A-F is going to hit, was narrowed to a hundred metre square. The evacuation began. Now HUMANITY, huddling far below the HORIZONS around me, as the RED glow overhead slowly grows, is a few minutes away from almost total incineration. The hammer of GOD is coming.
The first thing you'll notice is that some words are in capital letters. These are weight-words, carrying the sentence: When reading, you want to make sure that these words are read out with particular emphasis. This helps to stop you from stumbling over your sentences, or mis-reading things. Podcasters don't need to worry, of course, because you get multiple takes, but radio newsreaders aren't that lucky and clear indicators are important.
The next thing you'll spot is that all numbers have been spelled out. There is a good reason for this: 17045-2003AF can be read in a multitude of different ways, and trying to read it out loud will make you stumble (try it!): Do you read it "seventeen thousand and fourty five" or "seventeen oh fourty five". Is the dash silent, or is it integral to the message? These questions have to be addressed before you start reading out loud.
The final thing you'll spot is that some portions have been underlined. These sections are particularly difficult, or need special attention somehow. In this particular passage, "A-F" needs to be read out as "Ah Eff", rather than being a captitalised (and therefore emphasised) word of some sort. As such, a quick underline stops you from getting stumped when you get to that section of the text.
Urals is underlined as a bad example - you'd be unlikely to have trouble with a name that easy. However, foreign names, or words that are pronounced unexpectedly etc should be written down phonetically and underlined, which means they are treated differently by the reader. A non-native English speaker might wish to re-write "worcestershire sauce" as "woostershire sauce", to prevent the embarrassing, yet not uncommon mis-pronounciation this word often brings.
The final underlining is "RED glow overhead slowly grows", because it's a bit of a tongue-twister. Try reading it out loud. Generally, tongue-twisters should be re-written in radio copy. In this case, it would be tempting to re-write it as "red glow overhead grows", to minimise the gl-sl-gr twister.
In summary:
1) Spell out all numbers and abbreviations
2) Underline anything that might cause problems at reading time
3) Write down everything that needs it phonetically
4) Read everything out loud. If it doesn't sound right, it ain't
5) Shorten sentences.
6) Add commas wherever you can take a break. Don't worry about grammatically correct, people will never read your radio scripts: If you run out of breath half-sentence, it sounds strained and unprofessional
Finally, always read off paper or at worst an LCD screen. CRT monitors flicker, and your brain will 'fill in' gaps in a logical fashion, which means that all the hard work you have done on your script are out the window. All radio stations read news and bulletins off paper, and they seem to know what they are doing, most of the time.
Preparing your equipment and environment
Once you have a well-prepared script, it should be easy to present the work to the microphone. First of all, make sure you are talking past the mike, not into it. Some sounds in language (especially P and B sounds - known as plosives - and S and F sounds - known as wind letters) can cause a booming or popping sound if you talk directly into the microphone from too close a distance.
The next thing you want to do is to check the levels on your microphone. It is best if there is someone there to help you: On a professional mixing desk, you want the loudest part of your speech to hit just shy of -0 dB. That way, you don't get any distortion, and you get the loudest possible source recording. If you are recording digitally - directly into a computer, for example - microphones will often be auto-levelled, so you don't have to worry about it. If the software you are using has an EV meter, however, use it, and try to make sure that the sound isn't recorded too loudly.
The microphone should be on a stand: Mikes are sensitive pieces of equipment, and you don't want to be shuffling them about, playing with the microphone cord, or anything like that.
Once the microphone is completely set up, eliminate all background noise. In a professional studio this shouldn't be a problem, but in a home, it is never completely quiet: Computers humming, cars driving by, people listening to music nearby, etc. Closing windows and doors will help.
Finally, a drink of water is a good idea. Fizzy drinks are banned - you don't want to be burping in the middle of a presentation.
Reading your piece
With all the equipment ready and in place, and your scripts prepared, it's time to finally do some reading.
The most important rule to remember is to stay calm, and take your time. You've allotted 3 words per second, and the best thing would be to hit that target over the average of the piece. The ebb and flow of natural language will cause some fluctuations in reading speed, but this isn't a race, and if you read calmly and slowly you can scan ahead and be aware of what is happening later on in the text, keeping your eyes peeled for underlined or capitalised words.
Every comma should be a 1 to 2 'beat' break, and every full stop should be a 3 'beat' break, and new paragraphs should be around 5-6 'beats'. A beat, in this connotation, will be a syllable as part of your natural reading speed. If you at that point are reading quite fast, the breaks will be shorter, and vice-versa. Don't ever fall for the temptation of ignoring a comma or a full stop: If they sound wrong, take them out of the script, but learn to trust your own script: Once you start reading it out loud, the time of changes and revisions is gone. On-the-fly changes are a terrible idea, especially if you are new to reading things out loud.
If something goes wrong during the reading... If you aren't live on air, don't worry about starting and stopping the recording equipment: If you stumble over a word or a part of the sentence, just pause for a second, then start again at the beginning of the sentence. The engineers (or you, if you don't have any engineers at your beck and call) can edit it all into coherence later. If you are live on air, whatever you do, don't get fazed, don't get nervous, and don't apologise, unless you said something offensive. Just calmly repeat the word, and keep going. Remember that this is conversational, and most people wouldn't even notice.
Good luck!
Final notes:
If you are looking for a good piece of audio recording software, try the free Audacity (http://audacity.sourceforge.net/). It works on most platforms, and has most the basic capabilities you are likely to need.
World's fastest rapper: http://www.youtube.com/watch?v=kY543zxrLPo